Thermally insulated beverage containers have become increasingly popular with the public for use with hot beverages, such as coffee. Containers of this type may also be used for cold beverages as well. Hot beverages, such as coffee and tea, impose the most demanding thermal requirements on such a container. As a result, consumers have come to appreciate that double walled, vacuum insulated containers perform this function best. Such containers have sidewalls often manufactured from metal, particularly stainless steel to withstand the high mechanical loading due to atmospheric pressure. Thermally insulated beverage containers designed for keeping cold beverages from becoming, warm typically place a lower thermal load on the beverage container. As a result, such containers are often manufactured with a plastic double wall, wherein the interstitial space between the inner and outer walls is either thermally insulated with air or a foamed material.
In either case, it is highly desirable to provide a selectively openable lid for the beverage container. The lid performs at least two functions, the first of which is to prevent the beverage from spilling out of the container when the user is not actually drinking the beverage. This feature is particularly important when a hot beverage is in the container so as to prevent the user from becoming burned if the container tips over. As a second function, the lid should provide for drinking the fluid at a continual rate to prevent splashing or dribbling when the beverage is being drunk from the container. The lids for such containers are therefore typically provided with an open position, a closed position, and a third position in which the lid can be removed from the beverage container for cleaning. An example of a travel mug having a three-position, rotatable lid of the type described above is disclosed in U.S. Pat. No. 5,249,703 to Karp. That patent discloses a travel mug having two inwardly directly circumferential ears defining a gap region therebetween. A rotatable lid, having radially directed arms emanating from a central region at the bottom of the lid are adapted to pass through the gaps in the ears, and when rotated with the lid engage an underside of the circumferential rim of the lid with the radially inward directed ears. The rim is provided with diametrically opposed apertures to permit fluid to egress from the mug while air enters in through the remaining aperture to equalize pressure within the mug. The disclosure of this patent is incorporated herein by reference. One particular problem with this prior art design is that the drinking vessel must be specially manufactured with dedicated structure to engage the arms of the lid. In addition, although the lid is substantially splashproof when the lid is in the closed position, it is not leakproof if the mug is tipped over.
It has become increasingly common for users to employ thermally insulated beverage containers, particularly of the type best adapted for insulating hot beverages such as coffee, in moving vehicles, such as automobiles. One design branch in the prior art has attempted to provide a lid for such containers which is easily operated by a single hand between an open and closed position so that the user does not inadvertently spill a hot beverage on herself while driving her car. Lids of this type often employ a push button mechanism having a normally closed position. Examples of such prior art devices are shown in the following patents: U.S. Pat. No. 4,303,173 to Nergard; U.S. Pat. No. 3,964,631 to Albert; U.S. Pat. No. 3,967,748 to Albert; and U.S. Pat. No. 4,099,642 to Nergard. With respect to the lids disclosed in the above-identified patents, the user typically depresses a button near the rim of the lid to remove a stopper-like device from an aperture in the lid. Releasing the button returns the stopper to its normally closed position. Although devices of this type perform their intended function well, they have a significant unanticipated drawback. Specifically, the position of a stopper in a normally closed position provides an ideal breeding ground for bacteria in the junction between the stopper and the lid drinking aperture. In order to properly clean a lid of this type which quickly becomes fouled with such bacterial growth, the user must manually clean the lid by holding the mechanism open while using a brush or the like. It has been found that merely placing such lids in a dishwasher or the like will not adequately clean the area of contact between the stopper and the lid. Most users of this type of device find the requirement to manually wash the lid so inconvenient that they frequently will not purchase a second product of the same design.
Therefore a need exists for a splashproof and leakproof lid for an insulated beverage container which provides a truly leakproof and spillproof design in both an open and closed position, which does not encourage bacterial growth between moveable parts of the lid, and which is easily cleaned by the user.